The deadly march of Alzheimer's disease is slower in people aged 80 or older than the younger elderly, researchers have found.

The risk of developing Alzheimer's disease increases with age, and by 85, the risk is about 50 percent. But those who develop the progressive brain disorder that late in life will experience a less aggressive disease than those whose symptoms appear at 60 or 70 years, according to investigators at the University of California, San Diego.

Lead research Dominic Holland from the university's neuroscienes department said doctors will need to consider thse findings when assisting older patients for Alzheimer's disease.

"Methods for early detection, which will rely on biomarkers as well as mental ability, will need to take into account the age of the individuals being assessed," he said. Because the "old" elderly may deteriorate at a slower pace than younger patients, doctors may not realize these people as suffering from Alzheimer's disease.

The findings also have implications for clinical trials evaluating potential Alzheimer's treatments and cost-of-care projections for different Alzheimer's patients, Holland and other experts say.

Currently, no effective treatments exist to slow or cure Alzheimer's disease, which gradually destroys brain cells and robs people of memory, and their ability to communicate and carry out everyday tasks.